In flow control valves a device is utilized as the flow-controlling element, and may be provided in a variety of forms. The flow-control element may be actuated manually, or by other suitable indirect or powered means, and is typically positioned inside the valve so that the flow of fluids (e.g., including liquids, gases and plasma) can be modulated according to various application-specific requirements. In operation, the flow control element can be subjected to forces and moments from the fluids. These fluid forces and moments are a function of fluid pressure and flow rate. Appropriate actuation forces and moments are used to overcome the fluid forces and moments to provide for effective modulation of flow.
A typical flow-controlling element designs, such as a conventional ball valve, can change position (e.g., “drift”) when the ball is placed in some “throttled” position between fully open and fully closed. Some valves attempt to mitigate this tendency by providing a tighter friction fit between the ball and a complementary mating surface of a valve housing or body, called a “seat,” to maintain the valve ball in a desired position. Likewise, friction in a valve manual control handle assembly, and hydraulic forces internal to the valve ball, may be utilized to facilitate the valve assembly with maintaining the valve ball position in select fluid-flow positions.